WIRELESS M-BUS IN SMART GRID SCENARIO
KR HARIHARASUDHAN, Filippo COLAIANNI, Michele SARDO, Ramkumar S, Neha KOCHHAR
ABSTRACT
Energy demands increase day by day, and three main
activities address this growing request: optimization of the
energy mix, efficiency increases, and the Smart Grid. The
Smart Grid mixes different technologies to improve energy
management and increase communication on the energy
grid between energy suppliers and their final users, in a bidirectional way. This article describes the Wireless M-BUS
standard and how STMicroelectronics implements it based
on its own devices.
INTRODUCTION
The key player in the Smart Grid scenario is a smart meter –
an energy, gas and water meter with Automatic Meter
Reading (AMR) capability. The AMR introduces the
concepts of bi-directional communication with the local
meter and the energy provider, or utility company. Using
this technology, the energy customer is able to send in their
consumer bill, either periodically or on demand; on the
other side the energy provider is able to schedule
maintenance, connect and disconnect each user’s meter
remotely, and send, in real time, energy prices and tariffs.
One of the benefits of a smart metering system with
communication capabilities is the ability to use real time
metering data to generate and analyze energy consumption
patterns and peak energy demands of each individual
consumer. This information can be used by the utility as
well as the consumer. The utilities can offer dynamically
varying peak and off peak tariffs depending on the overall
load condition of the grid. On their part, consumers can
schedule their consumption of energy to run heavier loads at
off peak periods to benefit from reduced tariffs during those
times. The utilities benefit from not having to operate power
plants that produce power only during peak hours and lie
idle during the off speak hours. This improves the efficiency
of the system from the economic and reliability points of
view. In addition, automatic data collection reduces the
utility operator’s efforts in local reading and configuring
load distribution as well as reducing human errors.
Different kinds of network topology and connectivity are
possible between smart meters and energy providers; for
example, smart meters can exchange data, using Radio
Frequency (RF) or Power Line Communication (PLC), to
and from a local data concentrator, which can communicate
in real time with the utility using GPRS connectivity.
Moreover, the smart meter should be able to synchronize
and exchange information with other meters such as a water,
gas and heat meter, using proprietary or standard protocol.
Various standards are available for the implementation of
AMR.
WIRELESS METER BUS (WM-BUS)
The M-Bus (Meter Bus) is a common standard used for
AMR implementation, for remote energy meter reading. It’s
based on European standard (EN 13757-2 physical and link
layer, EN 13757-3 application layer). The M-Bus is
compliant with the European Standard EN 1434 on heat
meters, too. The M-Bus interface is made for
communication on two wires, a twist cable, making it very
cost effective. With the M-bus it is possible to use any kind
of network topology (linear, star, etc.), except ring network,
able to achieve long distance communication. When
interrogated, the meters send the data to a concentrator that
can be available locally or remotely.
A radio variant of the M-Bus, the Wireless M-Bus, is
also specified in EN 13757-4.
The Wireless M-Bus is an open standard for Automatic
Meter Reading at RF sub 1 GHz. The relevant standards
documents are the following:
European standard prEN13757-4:2011 Wireless
meter readout
European
standard
EN13757-3:2004
Dedicated application
layer (in common with M-Bus)
ETSI EN 300 220 v2.3.1
Fig1: Basic Wireless M-Bus Architecture
The Wireless M-Bus standard is defined by the European
standards EN 13757-4 for Physical and Data link layers.
The application layer is defined by EN 13757-3 standard.
The standard defines the communication between remote
meters and mobile readout devices, stationary receivers, and
data collectors. The typical application scenario is shown
below:
Fig 2: Final Application Scenario
The WMBUS standard is designed to give a long battery life
for battery operated meters, so that there won’t be any need
for battery replacement over the normal life span of the
meter.
A Wireless M-Bus can be mapped to an OSI Model in the
following way:
Table 1: Wireless M-Bus Mapped with OSI Layer
Host
Media
OSI Layer
Wireless M-BUS protocol stack
7. Application
EN 13757-3 Application Layer
6. Presentation
Not Used
5. Session
Not Used
4. Transport
Not Used
3. Network
Optional
2. Data link
EN 13757-4 Link Layer
1. Physical
EN 13757-4 PHY Layer
The data link layer of the EN 13757-4 standard supports two
different frame formats: frame format A and B. In a
standard Wireless M-Bus frame received, the data link layer
will immediately follow the preamble chip sequence. The
data link layer carries link layer data plus optional
application layer payload information. Except for the modes
C and F, the remaining modes support only frame format A.
For mode C and F, the frame format can be detected from
the pattern of the preamble chip sequence.
The Wireless M-Bus standard allows for the encryption of
the payload data using optimized encryption modes like the
AES 128 counter mode encryption.
STMicroelectronics has developed its own Wireless M-Bus
firmware stack implementation, based on its dual chip
platform: new SPIRIT1 RF Sub-1GHz transceiver and the
STM32L15 ultra low power, ARM Cortex-M3
microcontroller.
SPIRIT1
The SPIRIT1 is a very low-power and high performance RF
transceiver, addressing RF wireless applications in the sub-1
GHz band. It is designed to operate at 169, 315, 433, 868,
and 915 MHz. It supports the following modulations: 2FSK, GFSK, MSK, OOK, and ASK. The air data rate is
programmable from 1 to 500 kbps, dependent on the
selected modulation. It has an integrated SMPS that allows
very low power consumption: 9 mA in Rx and 21 mA in Tx
mode at +11 dBm. It uses a very small number of discrete
external components and integrates a configurable baseband
modem, which supports data management, modulation, and
demodulation. The data management handles the data in the
proprietary fully programmable packet format and also
allows the M-Bus standard compliance format (all
performance classes). The SPIRIT1 supports the low level
of WMBUS PHY protocol in hardware.
Some of the salient features of the Wireless M-Bus standard
are
1. Support for unidirectional and bi-directional
communication with the meter.
2. Support for different modes of communication (S,
C, T, R, F, N) depending upon the requirement of
the application.
3. Support for AES-128 CTR encryption for data
security.
4. Operation in both the license-free ISM and SRD
frequency bands at 169, 433, and 868 MHz
5. Provision for indicating faults and alarms.
More details can be found in the EN 13757-4 standard
document.
ST Ultra Low Power MCU: EnergyLite™ Family
For the physical layer, the EN 13757-4 standard also
specifies various performance classes depending upon the
maximum power to be transmitted and the lowest receiver
sensitivity that the meter provides.
In the WMBUS scenario, gas, water, and heat meters are
usually battery powered and require high energy efficiency
devices for long battery life; the EnergyLite™ family, 8-bit
(STM8L) and 32-bit (STM32L) MCUs, provides high
performance combined with ultra-low power.
Fig 3: SPIRIT1
The STM8L and STM32L offer specific features for ultra
low power applications, such as advanced ultra low power
modes, optimized dynamic run consumption, and specific
safety features. The ultra-low-power EnergyLite platform is
based on STMicroelectronics’ 130 nm ultra-low-leakage
process technology; they share common technology,
architecture and peripherals.
The STM32 L1 series, based on the ARM® Cortex™-M3,
extends the ultra-low power concept with no compromise in
performance. More than just ultra-low-power MCUs, the
STM32 L1 series offers a wide portfolio of features,
memory sizes and package pin counts. The portfolio covers
from 32 to 384 Kbytes of Flash memory (with up to 48
Kbytes of RAM and 12 Kbytes of true embedded
EEPROM) and from 48 to 144 pins.
This innovative architecture (voltage scaling, ultra-lowpower MSI oscillator) gives designs more performance for a
very low power budget. The large number of embedded
peripherals, such as the USB, LCD interface, OpAmp,
comparator, ADC with fast on/off mode, DAC, capacitive
touch and AES, gives the STM32 L1 series an expandable
platform to fit all requirements.
ST Wireless M-Bus Stack implementation, using
SPIRIT1 and STM32L
ST’s Wireless M-Bus stack, based on the EN 137574:2011.10 standard, supports the following modes:
Table 2: Wireless M-Bus Modes and Description
Mode
Communication
S1
Unidirectional
Frequency
Band
868 MHz
S1-m
Unidirectional
868 MHz
S2
T1
Bidirectional
Unidirectional
868 MHz
868 MHz
T2
R2
Bidirectional
Bidirectional
868 MHz
868 MHz
N1
Unidirectional
169 MHz
N2
Bidirectional
169 MHz
Description
Stationary mode: metering
devices send their data
several times a day. The
data collector may be
battery operated device and
optimized for stationary.
Same as S1, but the data
collector is mobile receiver
Bidirectional version of S1.
In the Frequent Transmit
mode, the meter devices
send the data every few
seconds to collectors in
range. The interval is
configurable (seconds or
minutes).
Bidirectional version of T1.
The Frequent Receive mode
permits multiple metering
devices not to interfere
using different frequency
channel.
This mode is optimized for
narrowband and long range
Bidirectional version of N1.
This mode doesn't support
N2g which requires 4GFSK modulation.
The WMBUS protocol stack is developed on ST’s dual chip
platform. The SPIRIT1 implements part of the WMBUS
physical layer, whereas the PHY and LINK firmware stack
layers are implemented by the STM32L15x, Ultra low
power ARM Cortex-M3.
STM32L role:
•
•
•
SPIRIT1 role:
•
WMBus Application Layer
WMBus Link Layer
•
MAC packet and CRC handling
•
Encryption/Decryption
initiate/read.
Wireless M–Bus PC GUI software is also available. Using
this PC-GUI makes it possible to monitor the status and
related energy consumption of each meter belong to the WMBUS network, configuring different WMBUS modality:
S, T, R, and N. The PC Software communicates with the
concentrator board or meter board using the USB HID
(Human Interface Device) Protocol. The protocol is bus
agnostic and can been ported to various transports, including
Bluetooth and other wired or wireless technologies. This
specification identifies the protocol, procedures, and
features for simple input devices to talk to HID over USB.
WMBus PHY
•
Init PHY for WMBus
•
Interrupt Services
WMBus Modes
•
Header, Sync and trailer fields
•
Manchester/3-out-of-6-encoding
•
Sync detection
•
Tx and RX FIFO
•
Data modulation and demodulation
•
RF TX and RX functions
Fig 5: Data Transfer from Meter to GUI
The data is displayed on the PC Software as shown below.
Below is the interface block diagram:
Figure 6: Data Display on the GUI
Figure 4: Application Diagram
The stack supports both meter and concentrator device
types.
To complete this scenario, a GAS Meter demo board with
WMBUS connectivity, 169 and 868 MHz – the STEVALIPG001V1 - will be available soon from ST.
Figure 7: Gas Meter Demo Board